1. Field of the Invention
The present invention relates to an X-ray imaging equipment for picking up two dimensional images based on a spatial distribution of X-rays transmitted through a subject and, more particularly, an X-ray imaging equipment having an X-ray flat panel detector.
2. Description of the Prior Art
In the prior art, there has been employed a general-purpose X-ray imaging equipment which comprises an I.I.-TV system having an image intensifier (abbreviated as "I.I." hereinafter) and a TV camera, and a film changer. Such X-ray imaging equipment is available in both an X-ray fluoroscopy and an X-ray radiography.
The X-ray imaging equipment is equipped with a diagnostic table on which a subject is put and which can move to stand and lay down. In a diagnosis of the digestive system, a contrast medium such as barium which is taken by the subject can be projected from various angles.
Normally such X-ray imaging equipments are classified into an over-table tube type X-ray imaging equipment (see FIG.1) wherein an X-ray tube is positioned over a tabletop of a diagnostic table and a detector is positioned below the tabletop when the tabletop is positioned horizontally, and an under-table tube type X-ray imaging equipment (see FIG. 2) wherein the X-ray tube is positioned below the tabletop and the detector is positioned over the tabletop when the tabletop of the diagnostic table is positioned horizontally.
The over-table tube type and under-table X-ray imagine equipment includes a diagnostic table 111, an I.I.-TV system 113, a film changer 115, a supporting body 117 and an X-ray tube 119.
In the over-table tube type X-ray imaging equipment employing the I.I.-TV system in the prior art, in the case that a chest radiography of the subject in an upright position of the diagnostic table is to be taken, a distance between the subject and an X-ray tube 119 can not sufficiently be kept because an I.I.-TV system 113 interferes with an inner wall of the building because of its size especially its depth.
Meanwhile, according to the normal imaging method in the chest radiography, an X-ray film or an X-ray detector is displaced in front of the subject in a standing position, and then an X-ray is irradiated to the subject from the back of the subject at a certain distance. However, in the case that the chest radiography is taken by the above over-table tube type X-ray imaging equipment, face or other portions of the subject interfere with a diagnostic table 111 when the subject tries to turn his or her back on the X-ray tube 119. Therefore, the chest radiography must be taken while turning the face of the subject laterally, which results in different postures of the neck and the chest of the subject from those in the normal radiography. In other words, it has been unreasonable to employ the above over-table tube type X-ray imaging equipment as the chest radiographic equipment.
In addition, in the X-ray imaging equipment in the prior art, the diagnostic table has not been able to be easily exchanged.
In the meanwhile, in the under-table tube type X-ray imaging equipment, an imaging device equipped with the I.I.-TV system 113 and the film changer 115 is provided over the diagnostic table 111, and the space between the imaging surface of the imaging device and the diagnostic table 111 is narrow in order to make the imaging surface close to the subject. Therefore, it is difficult for the subject whose physical strength is declined and the handicapped subject to get on or down from the diagnostic table 111 and further it is difficult for a doctor or a technical expert to get access to the subject.
Recently a technology of a thin and lightweight X-ray flat panel detector using a semiconductor technology has been disclosed (see U.S. Pat. No. 4,689,487).
This X-ray flat panel detector comprises semiconductor detector elements which are arranged to correspond to pixels aligned in a matrix fashion. The semiconductor detector elements detect X-ray directly, or indirectly in the form of visual light by means of fluorescent material, and then the detected X-ray is read as image signals via switching gates such as thin film transistors (TFTs), or the like.
The X-ray flat panel detector in which the X-ray is directly converted into a charge per pixel and then read out is called a direct conversion type X-ray flat panel detector. In contrast, the X-ray flat panel detector in which the X-ray is converted into visual light by the fluorescent material, etc., then the visual light is converted into the charge per pixel, and then read out is called an indirect conversion type X-ray flat panel detector.
FIG. 3 is a block circuit diagram showing a representative configuration of the indirect conversion type X-ray flat panel detector. Such X-ray flat panel detector detects two dimensional distribution of the light which has been converted from the X-ray to a visible light by the fluorescent material (not shown).
As shown in FIG. 3, each of the pixels which are arranged in a two-dimensional matrix fashion comprises a PIN photo diode (abbreviated as "PD" hereinafter) 81 for converting the intensity of the light into the charges and accumulating them, and a thin film transistor (abbreviated as "TFT" hereinafter) 82 as a switching device for reading the accumulated charges from the PD 81 as the image signal.
An anode of the PD 81 is connected to a common bias voltage (-Vn). A cathode of the PD 81 is connected to a source of the corresponding TFT 82. Respective gates of the TFTs 82 aligned on the same row are connected commonly to one of line driver signal lines 83 (83-1, 83-2, . . . , 83-n), and the TFTs 82 are driven sequentially into their reading state by a line driver 84. Respective drains of the TFTs 82 aligned on the same column are connected commonly to one of read signal lines 86 (86-1, 86-2, . . . , 86-n). The read signal lines 86-1, 86-2, . . . , 86-n are connected to a multiplexer 88 via charge amplifiers 87 respectively. The multiplexer 88 multiplexes signals output from the read signal lines 86-1, 86-2, . . . , 86-n and then outputs them as an imaging signal output 89.
When the TFTs 82 are set into their reading state by driving sequentially the line driver signal lines 83-1, 83-2, . . . , 83-n by the line driver 84 and supplying the voltage to the gates of the TFTs 82 on respective rows, the charges read out pixel by pixel are amplified by the charge amplifiers 87, then multiplexed by the multiplexer 88, and then output as X-ray image signals. The line driver 84 and the multiplexer 88 are controlled by a controller 91.
As described above, according to the over-table tube type X-ray imaging equipment employing the I.I.-TV system in the prior art, there has been such a problem that, if the chest radiography of the subject is to be taken in an upright position of the diagnostic table, a sufficient distance between the subject and the X-ray tube can not kept because the I.I.-TV system interferes with an inner wall of the building because of its size, especially its depth.
Further, if the chest radiography is to be taken by the above over-table tube type X-ray imaging equipment, the face, etc. of the subject interfere with the diagnostic table when the subject tries to turn his or her back on the X-ray tube. Therefore, there has been another problem that the subject cannot assume the normal posture for the chest radiography.
Furthermore, in the X-ray imaging equipment in the prior art, there has been still another problem that exchange of the diagnostic table is not ready.
Moreover, in the under-table tube type X-ray imaging equipment employing the I.I.-TV system in the prior art, the space is narrow between the diagnostic table and the imaging surface of the I.I.-TV system and the film changer. Therefore, there has been yet still another problems that it is difficult for the subject whose physical strength is declined and the handicapped subject to get on or down from the diagnostic table and it is difficult for a doctor or a technical expert to get access to the subject.